1. Field of the Invention
The present invention relates to threaded fasteners such as screws, bolts and nuts, and more particularly, to anti-cross threading fasteners.
2. Description of the Related Technology
Threaded fastener technology is basic to the construction or fabrication of most articles of manufacture such as machines, automobiles, trains, planes, engines, and the like. Threaded fasteners may be bolts, screws, studs, rods, or other substantially round members having uniform, non-uniform or tapered external helical threads that are screwably engaged into mating threaded fasteners such as nuts, bolts or holes having substantially matching internal helical threads. For proper engagement of the externally and internally threaded fasteners, the longitudinal axis of the externally threaded member must be substantially collinear with a longitudinal axis of the mating internally threaded member. When the externally threaded member is not substantially collinear with the internally threaded member, cross-threading occurs.
Cross-threading generally occurs when there is misalignment between the externally threaded member, typically a screw or bolt, and the internally threaded member, typically a nut or other threaded hole. Specifically, cross-threading is the result of the threads of the two members attempting to engage at least one-half pitch out of alignment. When this situation happens, the two members are not collinear with each other and wedging of the threads will occur as the threaded helix are rotated against each other. If rotation continues, then threads on one or both members will be structurally damaged.
Current art typically has a lead thread, i.e., first thread pitch, which grows gradually from the minor diameter to the full height over one-half to two thread turns. The lead thread is therefore usually somewhat shorter than the full thread in any section and generally follows the helical path of the thread. The disadvantage of this configuration is found in its tendency, at angles of axial misalignment, to become trapped behind a mating female thread when the helix is engaged. This trapping happens where the lead thread has reached such a height as to not move freely under the opposing thread, and thus prevent the two helix from attaining axial alignment.
Referring to FIGS. 1A through 1F, a typical lead thread is shown. In particular, FIGS. 1A through 1E are cross-sectional side views of the lead in thread and several adjacent full threads of a fastener, taken at 0xc2x0, 90xc2x0, 180xc2x0, 270xc2x0, and 360xc2x0 of rotation, respectively. FIG. 1F shows an end view of a fastener where points A, B, C, D and E correspond to the same characters in the other figures. In FIG. 1A, the lead thread begins to grow from the shank of the fastener. Through 90xc2x0 of rotation, the lead thread grows to a height as indicated by reference character B. Through 180xc2x0 of rotation, a cross-sectional side view of the fastener is shown in FIG. 1C. Here the lead thread has grown to a height which exceeds the pitch diameter. At 270xc2x0 of rotation, the cross-sectional side view of the fastener is shown in FIG. 1D. The highest point of the lead thread is indicated by reference character D in both FIGS. 1D and 1F. In FIG. 1E, a cross-sectional side view of the fastener is shown where the fastener is rotated 360xc2x0 from the position shown in FIG. 1A. In this view, the lead thread has grown to its maximum height as indicated by reference character E so as to merge into and become part of the first full thread.
In the fastener illustrated in FIGS. 1A through 1F, the lead thread grows from its minimum height to its maximum height over 360xc2x0 of rotation. Alternative embodiments of fasteners will have shorter or longer lead threads depending upon the pitch of the fastener. For example, a fastener having a very long pitch, will have a very short lead thread, wherein the lead thread will grow from its minimum height to its maximum height over 120xc2x0-180xc2x0 of rotation. Alternatively, in a fastener where the pitch is very short, it is possible for the lead thread to spiral around the shank of the fastener for several rotations far exceeding 360xc2x0 of rotation.
Referring to FIG. 2, cross-sectional, side views of a male threaded fastener bolt 10 and a female threaded fastener nut 22 are shown. The bolt 10 has a typical lead thread 1 located at the distal end of the bolt 10. The longitudinal central axis of the bolt 10 and nut 22 are shown in misalignment. In this position, the first full thread 20 of the bolt 10 is shown engaged with the lead thread of the nut 22. The lead thread 1 of the bolt 10 is shown immediately adjacent to the first full thread 30 of the nut 22. Because the lead thread 1 is already tall enough so as to not pass freely below and past the first full thread 30 of the nut 22, a cross-thread condition will occur upon further engagement of these fasteners. In particular, because the lead thread 1 of the bolt 10 extends to the exterior side of the first full thread 30 of the nut 22, it has no opportunity to move to the interior side of the thread 30 so as to bring the fasteners 22 and 10 into axial alignment.
What is needed is a fastener that prevents cross-threading when an-externally threaded member engages an internally threaded member.
It is therefore an object of the present invention to prevent cross-threading when an externally threaded member engages an internally threaded member.
Another object is to correct misalignment (non-collinearity) between two screwably attachable members having mating helical threads thereon.
Another object of the present invention is to easily correct misalignment that may cause cross threading of a threaded fastener.
The present invention is a lead thread which, while remaining inside the profile of the standard thread, moves to its forward edge so as to insure that at such time as it reaches a height that it might interfere with the female profile, it is not trapped behind the female thread. This lead thread may have any shape that effectively places it under or in front of the female thread when it reaches the appropriate height. The inventive thread may be used by itself with standard threads or may be used in combination with other anti-cross threading threads.
Yet another object of the present invention is to correct misalignment between a first fastening member and a second fastening member by having one or more threads of the first member cam over the threads of the second member, thereby bringing the first and second 20 members into collinear alignment.
Still another object is to use a protruding diameter feature at one end of the first member to restrict the misalignment angle between the two members.
In an embodiment of the present invention, a self alignment anti-cross threading fastener comprises a substantially round first member such as, for example, a bolt or screw, having an external helically wound thread on the shank of the first member. At one end of the first member shank is a head adapted to be engaged by a means for applying rotational torque. The head may be slotted to receive a flat, Phillips, Torx head and the like screwdriver blade, or may have a plurality of flat surfaces parallel with the longitudinal axis of the first member shank for receiving a wrench, socket or other means for rotationally engaging the head.
At the other end of the first member shank, the first preferably at least one helical thread has a transitionally curved surface from the minor diameter to the major diameter. The transitional curved surface of the first at least one helical thread of the first member is adapted to cam over the mating component threads of the second member when in a cross-threading position, thereby collinearly aligning the first and second members together.
In another embodiment of the invention, the end of the first member opposite the head may have a protruding diameter feature, commonly referred to as a dog point. This protruding diameter feature restricts the range of presentation angles when the first member is inserted into the second member. Thus, the inherent misalignment may be restricted so that the first at least one helical thread having the transitionally curved surface may easily cam over the mating component threads so as to rapidly bring the two members into the correct collinear alignment wherein the remaining threads of the first and second members rotationally engage to properly fasten as intended. The curved surface on the transitional threads may be formed by rolling the threads in a rolling die having a mirror image contour of the curved surface desired on the threads. The transitional thread curved surface may also be formed on the threads by cutting, burnishing, grinding, machining, polishing, laser, or any combination thereof
In still another embodiment of the present invention, at the end of the first member opposite the head, the first preferably at least one external helical thread has a transitional curved surface, or any combination of curved and/or flat surfaces approximating the shape defined by the curved surface, from the curve forming the minor diameter to the localized major diameter. The major diameter being defined as the outermost point of the helical thread in any localized axial section. The thread surface of the first at least one transitional thread is thus adapted to cam over the mating component threads of the second member when in a cross threading condition, thereby collinearly aligning the first and second members together.
In another embodiment of the present invention, at the end of the first member opposite the head, the first preferably at least one external helical thread has a truncated thread profile, approximating the shape formed by a radius drawn tangent to both thread flanks at their intersection with the curve forming the minor diameter. The minor diameter being defined as the innermost point of the helical thread in any localized axial section. The peak of the truncated thread may be flat or curved and maybe parallel to, or angled in relation to the screw thread axis. The thread surface of the first at least one transitional thread is thus adapted to cam over the mating component threads of the second member when in a cross threading condition, thereby collinearly aligning the first and second members together.
In a further embodiment of the present invention, a self aligning, anti-cross-threading fastener comprises a nut or other threaded member, having a helically wound thread on the interior of the member. The first preferably at least one internal helical thread has a transitional curved surface, or any combination of curved and/or flat surfaces approximating the shape defined by the curved surface, from the curve forming the major diameter to the localized minor diameter. The minor diameter being defined as the innermost point of the helical thread in any localized axial section. The thread surface of the first at least one transitional thread is thus adapted to cam over the mating component threads of the second member when in a cross threading condition, thereby collinearly aligning the first and second members together.
In another embodiment of the present invention, a self aligning, anti-cross-threading fastener comprises a nut or other threaded member, having helically wound threads oil the interior of the member. The first preferably at least one internal helical thread has a truncated thread profile, approximating the shape formed by a radius drawn tangent to both thread flanks at their intersection with the curve forming the major diameter. The major diameter being defined as the outermost point of the helical thread in any localized axial section. The peak of the truncated thread may be flat or curved and may be parallel to, or angled in relation to the screw thread axis. The thread surface of the first at least one transitional thread is thus adapted to cam over the mating component threads of the second member when in a cross threading condition, thereby collinearly aligning the first and second members together.
A feature of the present invention is a transitional curved surface from the minor diameter to the major diameter of the first at least one external thread of a first member, whereby the external thread surface area cams over the mating component threads of a second member and thereby collinearly realigns the first and second members together.
Another feature of the present invention is a protruding diameter feature, commonly referred to as a dog point, for restricting the presentation engagement angle of the two members.
Another feature is a self aligning, anti-cross-threading fastener having helically wound threads on the interior of the fastener.
Another feature is the transitional curved surface of at least one of the helical threads comprising any combination of curved and/or flat surfaces approximating the shape defined by the curved surface, from the curve forming the major diameter to the localized minor diameter.
An advantage of the present invention is a reliable and simple way of preventing cross-threading of a threaded fastener.
Another advantage is quick and reliable collinear alignment of a threaded fastener when rotatably engaging the threaded fastener by machine or unskilled labor.
Other and further objects, features and advantages will be apparent from the following description from the presently preferred embodiment of the invention, given for the purpose of disclosure and taken in conjunction with the accompanying drawings.